Circuits for cathode-ray tubes



March 3 A. w. VANCE 2,

CIRCUITS FUR CATHODE RAY TUBES Filed Sept. 29, 1934 2 Sheets-Sheet l YTIME g v t' ass c I 50 Operation,

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u V TIME TIME .ZNVENTUR ArthurWVa-nce HT'TORN Y Mmh 23,1937. f AWVANCE'2,074,495

CIRCUITS FOR CATHODE RAY TUBES Filed Sept; 29, 1954 2 Sheets-Sheet 2INVEN'I'OR Arthur W Vance Patented Mar. 23, 1931 PATENT OFFICE cmcorrsron. canons-my 'runns Arthur W. Vance,

mesne ents, America, New York, Delaware Philadelphia, 1a., assignor, by

to Radio Corporation of N. Y., a corporation of Application September29, 1934, Serial No. 748,098

8 Claims.

My invention relates to cathode-ray tube apparatus and particularly to amethod and means for obtaining a, high voltage. w

One of the problems in designing a system in which a cathode-ray tube isutilized is that of obtaining the necessary high voltage for the tubeelectrodes, especially for the second anode of a common type tube.Although there is no particular difliculty in merely obtaining thedesired voltage, the resulting voltage supply unit is usually rathercostly. The transformer for stepping up the voltage of 60 cycle currentfrom 110- volts to 4000 volts, for example, is an expensive unit. It isaccordingly an object of my invention to provide an improved method andmeans for obtaining a high voltage.

More specifically, it is an object of my invention to provide a methodand means for obtaining high voltage direct current for the second anodeof a cathode-ray tube.

A further object of my invention is to provide an improved deflectingcircuit for cathode-ray tubes.

In practicing my invention, I utilize the high voltage which is producedby the sudden collapse of flux in an; inductance coil. Specifically, incathode-ray tube apparatus wherein the tube is provided with defiectingcoils, I connect a rectifier circuit across the said coils whereby thehigh voltage produced across them during the flow of saw-tooth currenttherethrough is rectified. The rectified high voltage current charges acon denser which supplies the desired high voltage to the second anodeof the cathode-ray tube.

Other objects, features and advantages of my invention will appear fromthe following description taken in connection with the accompanyingdrawings, in which- Figure l is a circuit diagram of one embodiment ofmy invention,

Figs. 2, 3 and 4 are curves which are referred to in explaining myinvention, and

Figs. 5, 6 and 7 are circuit diagrams of other embodiments of myinvention.

In Fig. 1 my invention is shown applied to a television receiver whichincludes a cathode-ray tube I. The particular cathode-ray tubeillustrated is of a well-known type comprising an evacuated envelope 3having an electron gun therein which consists of an indirectly heatedcathode 5, a control grid 1 and a first anode 9. A second anode H,consisting of a silver coating on the inside of the envelope 3, isprovided for accelerating the electrons and for aiding in theelectrostatic focusing. The usual fluorescent screen I3 is provided atthe large end 01 the tube.

In accordance with common practice, the cathode-ray tube is providedwith one pair of deflecting coils l5 for deflecting the electron beamhorizontally and another pair of deflecting coils I! for deflecting theelectron beam vertically, whereby the fluorescent screen l3 may bescanned to produce a picture.

The horizontal deflection is produced by a flow or current, having asaw-tooth wave form, through the deflecting coils l5. The circuit forproducing this flow of saw-tooth current includes an electric dischargetube It which may be a three-electrode vacuum tube having a cathode 2l,a control grid 23 and an anode 25. The control grid 23 is maintained ata suitable negative bias by means of a source of biasing potential,suchas a biasing battery 21, connected in series with a grid resistor29.

The anode 25 is maintained at a suitable positive potential by means ofa suitable supply source, such as a battery 3|, the positive potentialbeing applied to the anode 25 through a choke coil 33. In thisparticular embodiment of the invention, the deflecting coils l5 areconnected across the choke coil 33 through a conductor 35 and a couplingcondenser 31, the coupling condenser 31 having suflicient capacity tomake its impedance at the horizontal deflecting frequency very low.

I The operation of the circuit thus Iar described will be understood byreferring to the curves shown in Figs. 2, 3 and 4. In Fig. 2 the curveE; represents the voltage which is impressed' upon the input terminalsof the vacuum tube 19 from a suitable generator or vacuum tube network20 for producing a flow of saw-tooth current through the deflectingcoils IS. The current flowing through the deflecting coils I5 isrepresented by the ,curve in in Fig. 3. It will be noted that thevoltage represented by the curve in Fig. 2 has two components, oneconsisting of 9, series of fiat-top impulses and the other consisting ofa saw-tooth voltage, the saw-tooth component being necessary forproducing a good saw-tooth current in the deflecting coils because ofthe plate impedance of the vacuum tube i9 and because of a small amountof resistance in the deflecting coils l5.

As shown by the curve E1. in Fig. 4, a very high voltage appears acrossthe deflecting coils i5 during what its commonly referred to as thereturn line period". In accordance with my invention I utilize this highvoltage'ior supplying the second anode II with the necessary highvoltage.

Referring again to Fig. 1, the circuit for obtaining the secondanodevoltage includes a rectifier 39- having a cathode M and an anode43, the cathode 4| being supplied with heating current from'any suitablesource through a transformer 45.

The rectifier 39 is connected across the deflecting coils I5 in serieswith a resistor 41 and a filter condenser 49. The rectifier circuit maybe traced from the upper terminal of the deflecting coils I 5 throughthe resistor 41 and the rectifier tube 39 to the mid-point of thesecondary winding of the transformer 45 and from the secondary mid-pointthrough the filter condenser 49 to the lower terminal of the deflectingcoils I5. The resistor 41 is provided in order to prevent the rectifiertube 39 from putting too great a load across the deflecting coils I5.With certain types of rectifiers it may be omitted.

It will be evident that the positive voltage im pulses appearing acrossthe deflecting coils I5 cause a flow of current through the rectifiertube 39 to charge the filter condenser 49. By connecting the secondanode I I to the positive terminal of the filter condenser 49 or to apotentiometer 5| shunted across the condenser 49, it is maintained at ahigh positive potential with respect to ground.

It will be noted that the voltage of the plate battery 3| is in serieswith the voltage appearing across the filter condenser 49 so that thetwo voltages add to give the total voltage applied to the second anode.It may be stated that the second anode current of the cathode-ray tubeillustrated is very small so that ample high voltage energy is suppliedby the deflecting coils I5 without placing too great a load across them.

The circuit shown in Fig. 5 differs from that shown in Fig. 1 in thatthe lower terminal of the deflecting coils I5 is connected to ground. Inthe two figures like parts are indicated by the same reference numerals.Where the deflecting coils are connected to ground it is preferred toconnect the rectifier resistor 41 on the anode side of the couplingcondenser 31, as illustrated, in

order that the voltage of the plate supply battery 3| will be added tothe voltage appearing across the filter condenser 49.

The circuit shown in Fig. 6 difiers mainly from the other embodiments ofmy invention in that the voltage appearing across the deflecting coilsI5 is applied to the rectifier through a transformer 53. In Figs. 1 and6 like parts are indicated by the same reference numerals.

Referring to Fig. 6, the circuit includes the transformer 53 having aprimary winding 55 and a secondary winding 51. The primary winding 55 isconnected across the deflecting coils I5. One terminal of the secondarywinding 51 is connected to one terminal of the filter condenser 49through a conductor 59 while the other end of the secondary winding isconnected to the other terminal of the filter condenser 49 through theresistor 41 and rectifier. 39.

By utilizing the transformer 53, the filter condenser 49 may be chargedto higher voltages then would be feasible if the maximum voltageobtainable were limited to the voltage appearing across the deflectingcoils I5. It is preferred to connect the primary of the transformer 53across the horizontal deflecting coils rather than the verticaldeflecting coils since the voltage impulses appear thereacross at acomparatively high frequency. This makes possible a ve y economicaltransformer design since a transformer transfers energy much better athigh frequencies than at low frequencies.

In addition to the feature of supplying a high voltage, my invention hasan additional advantage in that it improves the operation of thedeflecting circuit. In my copending application, Serial No. 741,230,filed August 24, 1934, and assigned to the RCA Victor Company, Inc., Idescribe and claim a cathode-ray tube deflecting circuit in which thedeflecting coils are shunted by a resistor in order to obtain greaterdeflection. In that circuit the deflecting coils discharge through theresistor, instead of through the vacuum tube, during the return lineperiod whereby the vacuum tube is given a period in which to cool. Onedisadvantage of the circuit is that during the deflection period acertain amount of current flows through the resistor which is in shuntto the deflecting coils to produce an undesired energy loss.

In my present circuit'the rectifier circuit is shunted across thedeflecting coils in place of a simple resistor whereby the deflectingcoils will discharge through the rectifier during the return line periodto reduce the load on the vacuum tube. It will be apparent, however,that there can be no flow of current through the rectifier circuitduring the deflecting period to produce an energy loss such as the onementioned above.

Preferably the present circuit is operated in the manner described in myabove-mentioned copending application to give what is substantiallyClass C operation. When operated in this manner the voltage impulsesapplied to the input circuit 'of vacuum tube I9 are given a magnitudesuificient to drive the vacuum tube I9 beyond the cut-ofi point(indicated by the dotted line 50 in Fig. 2) whereby the deflecting coilsI5 discharge only through the rectifier circuit. It may be noted thatthe return line portion of the sawtooth wave shown in Fig. 3 departsfrom a straight line and that the voltage impulses shown in Fig. 4 arenot flat topped because of the discharge of the deflecting coils I 5through the rectifier circuit, this being a logarithmic discharge.

As illustrated in Fig. 7, where parts similar to those in Fig. 1 areindicated by like reference numerals, a rectifier may be connectedacross the deflecting coils I5 solely for the purpose of increasing themagnitude of deflection with a given size vacuum tube in accordance withthe teachings of my above mentioned copending application. In thisembodiment of my invention, the condenser 49 is omitted, the secondanode I I being supplied with a high positive voltage from any suitablesource (not shown).

Considering my invention as a circuit for supplying a high voltagewithout the use of a transformer, it. will be understood that it is ofgeneral application and is not limited to a cathode-ray tube deflectingcircuit. Any suitable conductors may be utilized in place of deflectingcoils.

It will be apparent that various other modifications may be made in myinvention and I desire, therefore, that only such limitations shall beplaced thereon as are necessitated by the prior art and set forth in theappended claims.

I claim as my invention:

1. In cathode-ray tube apparatus, a cathoderay tube having deflectingcoils, means for producing a flow of saw-tooth current through saidcoils whereby voltage impulses appear thereacross, and means forderiving a unidirectional voltage from the voltage impulses appearingacross said coils.

2.. In cathode-ray tube apparatus, a cathoderay tube of the type havinga second anode, de-

said horizontal deflecting coils whereby a unidirectional voltageappears across said capacitor.

6. In apparatus comprising a cathode-ray tube having deflecting coils, arectiflerconnected across flecting coils for said cathode-ray tube,means said coils, and a vacuum tube having its output 5 for producing aflow of saw-tooth current through circuit coupled to said deflectingcoils, the methsaid coils whereby voltage impulses appear 0d of causingaflow of deflecting current through thereacross, means for deriving aunidirectional said coils which includes the step of periodicallyvoltage from the voltage impulses appearing driving said vacuum tube toplate current cutacross said coils, and means for applying said off. 1unidirectional voltage to said second anode. 7. In combination, acathode-ray tube having 3. In combination, a cathode-ray tube,deflectdeflecting coils, a vacuum tube having a control ing coils forsaid tube, means for producing a electrode and an output circuit, saidoutput cirflow of deflecting current through said coils, said cuit beingcoupled to said deflecting coils, means means including an electricdischarge tube havfor impressing negative voltage impulses period- 15ing an output circuit connected to said coils, ically upon said controlelectrode whereby enand a circuit including a rectifier connected ergyStored in Said 60115 tends to discharge across said coils. through saidvacuum tube for the duration of 4. The invention according to claim 1chareach of said impulses, and means connected in acterized in that saidlast means comprises a, shunt to said coils to reduce the amount of said20 rectifier and a capacitor c'onnected in. series St re e y whichdischarges ou S d across said coils. vacuum tube.

5. In a television receiver including a cathode- I cathode-ray tube pp ua th d ray tube provided with both horizontal and very be, deflecting0011s for d tube. means for tical deflecting coils and in which voltageimproducing a flow oi. saw-tooth deflecting cur- 2 pulses are applied tosaid horizontal deflecting rent through said coils, and a rectifierconnected coils at a more rapid rate than to said vertical across saidcoils for deriving a unidirectional deflecting coils for causing anelectron beam to voltage from the voltage impulses appearing scan afluorescent screen, a rectifier and a cathereacross. pacitor connectedin series and shunted across 30 ARTHUR W. VANCE.

CERTIFICATE OF CORRECTION.

Patent No 2, Q7 b -l-95.

March 2 19 7.-

ARTHUR w. VANCE.

It is hereby certified that error appears in the printedspeoification ofthe above numbered patent requiring correction as follows: Page 2,second column, line 62, for the word "conductors" read inductors; andthat the said Letters Patent should be read with this correction thereinthat the same may conform to the record of the case in the PatentOffice.

Signed and sealed this 16th day of November, -A. D. 1937.

Henry Van Arsdale,

(Seal) Acting Commissioner of Patents.

